Autonomous vehicles or highly automated vehicles include an operational mode in which a computing system is used to navigate and/or maneuver the vehicle along a travel route with minimal or no input from a human driver. Autonomous vehicles may allow for a manual override of the autonomous operational mode. Manual override may occur if a received input from the vehicle driver exceeds a predetermined threshold input level.
Some vehicles permit a semi-autonomous mode of operation in which a portion of the vehicle controls are operated autonomously but the rest of the vehicle controls are operated manually by a driver. For instance, in an adaptive cruise control system, the speed of a vehicle is automatically adjusted to maintain a safe distance from a vehicle ahead based on data received from on-board sensors, but the vehicle is otherwise operated in a manual mode. Upon receiving a driver input to alter the speed of the vehicle (e.g. by depressing the brake pedal to reduce the speed of the vehicle), the adaptive cruise control system is deactivated and the speed of the vehicle is reduced.